Implement segment and measure job

[dchaley]

This creates a job to run segmentation (DeepCell), followed by, measurement (QuPath).

✨ commit by commit review encouraged ✨

There's a lot along the way–

• Unify job launchers: refactoring how we set up job definitions.
• Unit tests. The arg parsing (etc) was getting a bit chaotic. It's important, so I started locking it down.
• Clean up & organization.

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Related to #294 – we'll see if it fixes it 😅 So far it ran the 2 jobs, but the qupath one didn't actually output anything 🤔

The logs say we uploaded the files:

But where are the files??